Studio Tests

The 12-24mm returns extremely good results in our studio tests, with impressive image quality across the range. Perhaps as a result of its more modest wideangle ambitions, it comprehensively outperforms both the Tamron 10-24mm F3.5-4.5 Di-II and the Sigma 10-20mm F4-5.6 EX DC HSM. Indeed overall it's arguably a better performer on APS-C than Olympus's ZD 9-18mm F4-5.6 is on Four Thirds - no mean feat.

Macro Focus

If there's one thing the Tokina 12-24mm isn't very good at, it's closeup shots. Maximum magnification is 0.13x, achieved at a minimum focus distance of 30cm, which equates to a working distance of 16cm from the subject to the front of the lens. Sharpness is poor wide open, with significant softening due to halation (not that unusual with internal focus zooms). Best results are obtained at F8 and F11, but the corners of our chart shot remain soft, suggesting strong curvature of field. Distortion is low, but there's quite strong blue/yellow chromatic aberration.

Macro - 186 x 123 mm coverage Distortion: Mild barrel Corner softness: High Focal length: 24mm (36 mm equiv)

FX (Full Frame) Coverage

Both the Nikon and Canon mount versions of this lens will mount on full-frame DSLRs; on Nikon cameras (D3, D3X, D700) DX crop mode will be automatically selected (and the camera will therefore shoot at reduced resolution). The lens's image circle obviously doesn't fully cover the 35mm full frame format at wideangle, but as is common for this type of lens, the vignetting progressively diminishes on zooming in, and coverage is complete at focal lengths of 18mm and longer (essentially affording the same widest angle of view on full frame as on DX). We're not going to formally test a DX lens on full-frame, but impressions are that the lens would be perfectly useable as an 18-24mm in an emergency or for non-critical applications.

12mm	15mm	18mm	20mm	24mm

Colour balance

Third party lenses have acquired something of a reputation for less-than-neutral colour balance, so in this test we measure any colour cast introduced by the lens in comparison to the camera manufacturer's 50mm lens (generally considered a good standard for neutrality). We've seen little evidence in our previous reviews of Sigma and Tamron lenses to support this reputation, but the 12-24mm is the first Tokina we have looked at.

In this test, the camera is pointed towards an evenly illuminated white wall, and light entering the lens completely diffused using an 'Expodisc' white balance filter. A custom white balance is taken using the 50mm lens (in this case the Nikon AF-Nikkor 50mm F1.4D), then exposures made using the 50mm lens and the lens under test. The Tokina 12-24mm F4 gave essentially no colour cast in comparison to the reference lens.

Nikon 50mm F1.4D (188, 188, 188)	Tokina 12-24mm F4 (184, 183, 183)

Specific image quality issues

As always, our studio tests are backed up by taking hundreds of photographs with the lens across a range of subjects, and examining them in detail. This allows us to confirm our studio observations, and identify any other issues which don't show up in the tests. The Tokina 12-24mm generally performed very well in normal use, with the only a certain susceptibility to flare really affecting the results.

Flare

Control of flare is a critical feature of a superwide lens; with such a broad view of the world, bright light sources will find themselves in the frame on a regular basis. However it's fair to say that this isn't the Tokina's strongest suit, and on a bright sunny day flare patterns can easily find their way into your images.

The most problematic flare artifacts tend to be strong orange-coloured spots in the extreme corners of the frame opposite the light source, which can be highly visible at all apertures from F4 to F11 when shooting at the wide end of the zoom range. These are illustrated in the examples below; in the second image flare spots are visible in both corners.

12mm F5.6, sun in corner of frame	12mm F5.6
50% crop, bottom right corner	50% crop, bottom right corner

Stop down further and this particular pattern tends to disappear, but a diagonal array of flare spots comes into prominence instead (below left). Zooming in slightly also eliminates this pattern, and as it's easily visible in the viewfinder, this makes it relatively straightforward to combat in use. Diagonal flare patterns can also be seen when the sun is out of the frame, but still impinging on the front element, and are visible at all focal lengths and apertures.

12mm F22, sun in corner of frame	24mm F4, strong backlight

To be fair Tokina claims that their new 'II' version of the lens uses a new, superior multi-coating system, so we'd hope that it addresses this problem, and outperforms the lens we tested in this regard.

Chromatic aberration

The other weakness of the Tokina 12-24mm F4 lies in its lateral chromatic aberration characteristics. Fringing is quite strong at 12mm, and most problematically is of the visually intrusive green/magenta variety in the corners of the frame (where it's naturally most pronounced). To compound the issue, though, it varies in colour across the frame, and in a fashion which changes with aperture. This can make software correction less than straightforward, as slightly different parameters are required for each focal length/aperture combination, and few programs can completely correct for this type of non-linear behavior.

The samples below illustrate this; at F4 the fringing is green/magenta in the corner, but blue/yellow further into the frame. Stop down to F8 and the corner fringing becomes visually more intense due to an increase in the red component; this also results in a change in fringe colour to green/magenta in the second crop.

12mm F4	12mm F8
Nikon D300, RAW + ACR
100% crop, top left corner
100% crop, upper left

This type of CA can be difficult to correct perfectly, and the crops below illustrate this using JPEGs from the Nikon D300. This camera (like most of its stablemates) automatically corrects lateral CA using a simple 'channel scaling' approach. In this example it's corrected the corner CA near-perfectly, but in the process generated problems with the inner crops; at F4 over-correction of the red channel combined with under-correction of the blue channel has produced strange orange/blue fringing artifacts in this region.

12mm F4	12mm F8
Nikon D300, camera JPEG
100% crop, top left corner
100% crop, upper left

Chromatic aberration becomes less of a problem as you zoom in, and by 24mm fringe widths have reduced substantially. The example below illustrates this, with crops taken from similar regions of the frame as above. Red/cyan fringing is visible in the extreme corner, but across most of the frame there's scarcely anything apparent at all. The D300's automatic correction algorithm has in this example taken a near-ideal course of action, slightly under-correcting in the extreme corners, and therefore not introducing significant problems elsewhere in the frame.

Nikon D300, RAW + ACR	Nikon D300 JPEG
24mm F8
100% crop, top left corner
100% crop, upper left

How problematic any of this will be in real-life use is open to question, and depends on the preferences of each individual user. It's also important to appreciate that the visibility of fringing is little different to that seen from many popular zooms such as the Nikon 18-200mm F3.5-5.6G VR or the Canon 18-200mm F3.5-5.6 IS; it's just more difficult to remove if desired. So if you're particularly allergic to chromatic aberration, and like to eliminate all traces of colour fringing from your images, this may not be the best lens for you.